Piranhas attacked at least 100 beachgoers this weekend in the Piaui state in northeast Brazil, according to UOL Noticias. The bathers were mostly bitten on their feet and were treated at a hospital near Terezina, the capital of Piaui. Though there have been sporadic attacks within the past two months, this weekend saw a sharp spike in piranha activity.

“Since they have no predators, piranhas have started attacking people on the beach,” environmental official Romildo Mafra told the Agence France-Presse.

These carnivorous river monsters are feared for their sharp, interlocking teeth, which they use to prey on smaller fish. They often hunt in schools, but if other fish are not readily available, they will occasionally resort to cannibalism to quell their hunger. However, attacks on humans are relatively rare, and biting is thought to be a mark of carelessness rather than planned assault. Put it this way: if they wanted to eat you, you would know it.

Piranha overpopulation is a continuing problem in this area of Brazil’s North Coast. Environmental officials have started adding tilapia to the piranhas’ waters in an attempt to satiate them, releasing 100,000 so far. An additional 200,000 fish will be released over the next several months. For now, bodysurfers and beachgoers beware.